Apparatus for electromagnetic radiation of living tissue and the like

ABSTRACT

Apparatus for electromagnetic radiation of living tissue, such as human tissue, or tissue simulating matter, comprises an electromagnetic radiation source having a dynamic frequency range of at least about 5 to 1, and preferably 10 to 1. Electrically connected to the source by a coaxial cable is a broadband applicator adapted for emitting electromagnetic radiation into tissue and the like. Parallel plate type radiation launching portions of the applicator are configured to have a characteristic impedance, throughout the dynamic frequency range, approximately equal to the impedance of specimens to be irradiated, which for human tissue, between 50 MHz - 2000 MHz, is approximately 50 ohms. A transition for interconnecting the coaxial cable to the parallel plate launching portion is configured to provide a relatively gradual coaxial to parallel plate transition at constant characteristic impedance throughout the dynamic frequency range. Both air filled and dielectric filled transitions and air filled, whole body and dielectric filled, partial body applicators are described.

This application is a division, of application Ser. No. 002,584, filedJan. 11, 1979, now U.S. Pat. No. 4,271,848.

The present invention relates generally to the field of apparatus forapplying electromagnetic radiation to human and animal tissue, and moreparticularly to broadband systems and transmission and applicatorportions of such systems adapted for medical use, for example forelectromagnetic radiation hyperthermia.

Hyperthermia or induced high body temperature in general has, for manyyears, been of considerable interest for treating cancer, as well asvarious other human diseases. Some types of malignant cells reportedlycan be destroyed by raising their temperatures to levels slightly belowthose injurious to most normal cells; hence, selective hyperthermia ispossible and is an area of continuing research. Also, some types ofmalignant cell masses lend themselves to selective hyperthermiatreatment because the masses of such malignant cells have much poorerheat dissipation characteristics than normal tissue (possibly due topoorer blood circulation therethrough), and hence can often be raised totemperatures substantially above that of surrounding healthy cells evenwhen both are exposed to the same heat source.

Certain types of malignant cells are generally considered to have arelatively narrow thermal treatment temperature range. For example, itis believed that below a threshold of about 41.5° C. (106.7° F.)insubstantial thermal destruction of certain malignant masses occurs. Athyperthermia temperatures below this 41.5° C. threshold, growth of somemalignancies may actually be stimulated. At temperatures above about 43°C. to 45° C. (109.4° F. to 113° F.) thermal damage to most normal cellsis known to occur. Of course, the time exposure to the particularelevated temperature is also determinative. If large or criticalportions of the body are heated into or above the 43° C. to 45° C.temperature range for too long a time, serious permanent injury or deathis possible.

Although some skin malignancies have been successfully treated byapplication of surface heat, due to body heat transfer properties,deeply located malignant growths can rarely be heated to the necrosistemperature in this manner without causing thermal damage to overlyingnormal tissue.

A promising alternate hyperthermia technique is electromagneticradiation (EMR) heating. Alternative electric currents at frequencieshigher than about 10 KHz were found in the late nineteenth century toproduce heating in human tissue, and were used to treat such disordersas diseased tissue and damaged muscles. In the early twentieth centurythe term "diathermia" was introduced to describe such tissue heating byconversion of high frequency electric currents into heat.

In 1933 hyperthermia treatment of malignant growths by high frequencyEMR was described by Dr. Schereschewsky in an article entitled"Biological Effects of Very High Frequency Electromagnetic Radiation"which appeared in RADIOLOGY in April of that year. Experimental EMRtreatment of tumors in mice at frequencies up to 300 MHz was reportedand a review of activity in the EMR diathermia/hyperthermia field waspresented.

More recently, in 1974, Guy, Lehman and Stonebridge presented ahistorical background of high frequency EMR hyperthermia and discussedcurrent experimental activity in the field in an article entitled"Therapeutic Applications of Electromagnetic Power", appearing in thePROCEEDINGS OF THE IEEE, Volume 62, No. 1, January, 1974.

A serious problem associated with EMR hyperthermia has, however, beencausing thermal necrosis of malignancies without excessively thermallydamaging adjacent healthy tissue, for example, by excessive EMRintensity or improper frequencies, or by standing waves resulting fromapplied EMR energy reflections at boundaries between body tissue layers.

Still requiring further definition and investigation are potentiallyharmful, low level, nonthermal EMR effects, considered to be caused byelectromagnetic forces acting on cell molecules, include realignment ofcell molecules into chain-like formations, tendency to coagulate cellmolecules, and possibly damage to normal cells resulting in a cause ofcancer, and in a myriad of other physiological effects.

Low level EMR has been observed to cause effects on central nervous andcardiovascular systems, such as decreased arterial pressure and reducedheart rate, the Soviets reporting such effects at radiation levels below10 milliwatts per square centimeter. A more thorough discussion of thesenonthermal effects is, for example, presented in an article by Johnsonand Guy, entitled "Nonionizing Effects of Electromagnetic Wave Effectsin Biological Materials and Systems" appearing in the PROCEEDINGS OF THEIEEE, Volume 60, No. 6, June, 1972.

Because of these potentially harmful and/or poorly understood nonthermalEMR effects, a maximum power density for prolonged EMR exposure has beenset at 10 milliwatts per square centimeter in the United States;whereas, the Soviets have established a maximum of 0.01 milliwatt persquare centimeter. In contrast, EMR hyperthermia and diathermy commonlyuse power densities as high as one watt per square centimeter,emphasizing necessity for more research in nonthermal EMR effects.

A serious problem in EMR hyperthermia research has, at least untilrecently, been lack of convenient, non-interfering apparatus foraccurately monitoring tissue temperature during irradiation.Conventional thermocouples typically have caused reflections of theapplied radiation, resulting in hot spots at unpredictable locations.And, because the incident EMR tends to bias the thermocouples,temperature readings have been suspected as being inaccurate.

Other substantial problems have been caused by available EMR researchapparatus being relatively inefficient, costly and inflexible.Typically, such apparatus has heretofore included ad hocinterconnections of standard components, such as EMR generators andtransmission lines of the type generally used in microwavecommunications, to applicators analogous to free space radiatingantenna. In consequence, mismatch of characteristic impedances (Z_(o))at various interfaces has caused radiation reflections limiting EMRsystem efficiency. Accordingly, the EMR source must ordinarily provideEMR power many times higher than the power actually to be applied to thespecimens to be irradiated. Although the resulting power loss may onlybe a few hundred watts, considerably more costly EMR sources arerequired than would be necessary for efficient systems.

More importantly, much of the power lost is typically radiated into thesurroundings from the transmission lines and applicators. Unlessextensive shielding, which restricts access to the apparatus isprovided, researchers are subjected to potentially harmful levels ofstray electromagnetic radiation.

When such EMR systems use only a single EMR frequency, or a very narrowrange of frequencies, efficiency can be somewhat increased bycompensating for impedance mismatches with "tuners". These tuners, whileprotecting the EMR source and increasing efficiency, however, causestanding waves in the system which in turn tends to increase radiationleakage near the radiating device.

However, for effective EMR studies using different geometric andcompositions of test bodies and for investigations involving tissuesheating and nonthermal effects at different depths and over differentbody areas, capability for radiating at frequencies over a broad dynamicrange of at least about 5 to 1 and preferably 10 to 1 is desirable.Although federal limitations has been placed on diathermy frequencieswhich can be used, to prevent interference with broadcasting andcommunications, because of the different manner of applying radiation inhyperthermia use, a chamber to prevent stray interference could be used.

Other problems have been associated with EMR applicators which havetypically provided poor EMR coupling into the test bodies. In additionto causing undesirable amounts of stray radiation, uniform or otherspecifically profiled EMR fields have been difficult to attain, and theapplicators have not had good broadband capabilities. As a result,tissue heating has generally been difficult to control and predict.

The present invention provides an irradiation system combination, aswell as separately useful components thereof, particularly adapted tomedical research, for example, in EMR hyperthermia, while providingefficient operation throughout a broad frequency range and avoiding someof the limitations of prior systems. Included in the apparatus of thepresent invention are efficient EMR applicators of both whole body andlocalized heating types. This apparatus also has important uses invarious fields of EMR irradiation research and application, includinginvestigation of and possible ultimate use for various types of diseasesand disorders, elevation of body temperature following hypothermiaconditions such as low temperature operations, and investigation ofnonthermal EMR irradiation effects on human and animal tissue.

In accordance with the present invention, a broadband electromagneticradiation system particularly adapted for irradiating living tissue andtissue simulating matter comprises the following: A broadbandelectromagnetic radiation source having an output impedancesubstantially equal to an average impedance of the living tissue, ortissue simulating matter to be irradiated, over a selected dynamicfrequency range of at least about 5 to 1 is coupled to a transmissionmeans also having a characteristic impedance approximately equal to theimpedance of the tissue or tissue simulating matter throughout thedynamic frequency range. An applicator for radiating, electromagneticenergy includes parallel plate-type launching means. The launching meanshas a characteristic impedance, when the applicator in operativerelationship with tissue or tissue simulating matter for irradiationthereof, approximately equal to the average impedance of the tissue ortissue simulating matter throughout the frequency range. Electricallyinterconnecting the transmission means with the applicator are broadbandtransition means for enabling substantially reflectionless transmission,throughout the dynamic frequency range, of electromagnetic waves fromthe transmission means to the applicator. The transition means isconfigured for having a characteristic impedance approximately equal tothe tissue and tissue simulating matter impedance throughout thefrequency range.

Because impedances of system components are substantially matchedthroughout the entire dynamic frequency range, broadband operation atgood efficiencies is enabled, as is important to limit radiation leakageand provide a comparatively economical system particularly adapted forresearch into electromagnetic radiation hyperthermia effects on livingtissue and other related, medically oriented fields.

In accordance with one embodiment of the invention, the transitionelement, which is also a separately useful component, is configured toprovide a substantially continuous transition between conventionalcoaxial cable, and parallel plate type transmission lines. The sourceend of the transition means is substantially coaxial cable-like inconfiguration and the parallel plate end of the transition means has aparallel plate-like configuration. Included in the transition means is afirst conductor configured to provide a smooth transition between acoaxial cable outer conductor and a first plate of the parallel plateend of the transition means, and a second conductor configured toprovide a smooth transition between a coaxial cable inner conductor anda second plate of the parallel plate end of the transition means.

Since the coaxial cable is ordinarily small in diameter, the transitionmeans also preferably includes diverging means at the coaxial cable endfor increasing the size of at least one of the conductors, whilemaintaining the characteristic impedance of the transition meansthroughout the dynamic frequency range.

The transition means may be either air filled or dielectrically filled,and is also adapted, although not at constant characteristic impedance,for providing transition between coaxial and parallel plate transmissionlines having different impedances, as may sometimes be necessary.

Also in accordance with one embodiment of the present invention, andconstituting also a separately useful component, the applicator includesa radiating chamber having parallel, spaced apart top and bottomconductive plates, with a first conductive end plate interconnectingfirst ends of the top and bottom plates. Further, a second conductiveplate, having a first end connected to a second end of the top plate,has a height equal to at least about half the spacing between the topand bottom plates. Radiating ends of first and second launching meansplates, which converge in width and separation to maintain constantcharacteristic impedance, are connected, respectively, to the secondends of the second end plate and the bottom plate.

The length of the resonator chamber is equal to about one half thewavelength of a selected electromagnetic radiation frequency within thedynamic frequency range so that standing electromagnetic waves arecreated within a resonator cavity.

For an alternative type of applicator in accordance with the invention,the launching means thereof is dielectrically filled and includes firstand second electronically conductive, opposing walls each having asource end connected to included transition element conductors. Width ofthe walls and separation therebetween is increased towards the emittingends thereof to maintain a substantially constant characteristicimpedance at substantially all transverse sections, over aelectromagnetic dynamic frequency range of at least about 5 to 1. Theapplicator includes a field coupling means, which in turn includes firstand second conductive flaps connected to the emitting ends of thelaunching means walls for improved radiation coupling with tissue andtissue simulating matter being irradiated.

For further improved radiation coupling and heating, a plurality of theabove mentioned alternative type may be arranged in flap overlappingrelationship around tissue or tissue simulating matter, for example ahuman limb, to thereby form a radiating cavity loaded by the tissue tobe irradiated. In this manner, improved electromagnetic radiation deepheating is provided in central regions of the tissue mass.

A better understanding of the present invention may be had from aconsideration of the following detailed description, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a broadband electromagnetic radiationapparatus, according to the present invention, for irradiating livingtissue or tissue simulating material;

FIG. 2 is a perspective drawing of coaxial to parallel plate transitionmeans portions of the apparatus of FIG. 1;

FIG. 3 is a sequence of transverse sectional views, taken along line3(a)--3(a) through 3(g)--3(g) of FIG. 2, showing enlargement of coaxialend portions of the transition means and showing the coaxial to parallelplate transition;

FIG. 4 is a perspective drawing of an alternative, dielectrically filledcoaxial to parallel plate transition means;

FIG. 5 is a sequence of transverse sectional views, taken along lines5(a)--5(a) through 5(f)--5(f) of FIG. 4, showing enlargement of coaxialend portions of the transition means and showing the coaxial to parallelplate transition;

FIG. 6 is a partially cutaway perspective drawing of an whole bodyelectromagnetic radiation applicator according to the present invention,showing incorporation of the transition means of FIG. 2;

FIG. 7 is a partially cutaway, side elevational view of the applicatorof FIG. 6, showing features thereof;

FIG. 8 is a partial, top plan view of the applicator of FIG. 6, showingtransition means and launching means portions thereof;

FIG. 9 is a sequence of transverse sectional views, taken along lines9(a)--9(a) through 9(c)--9(c) of FIG. 8, showing width and spacingdivergence of the launching means portion;

FIG. 10 is a perspective drawing of an alternate, dielectrically filled,partial body applicator incorporating the dielectrically filledtransition means of FIG. 4;

FIG. 11 is an elevational cross sectional view of the dielectricallyfilled applicator of FIG. 10, showing the applicator in operationalrelationship with portions of a body or test specimen;

FIG. 12 is a transverse sectional view along line 12--12 of FIG. 11,showing features of the dielectrically filled applicator;

FIG. 13 is a drawing similar to FIG. 11, showing a pair ofdielectrically filled applicator positioned in partial overlappingrelationship around portions of a body or test specimen; and

FIG. 14 is a plot of efficiency Vs. frequency for dielectrically filledapplicator of the type shown in FIG. 10.

As seen in FIG. 1, a broadband electromagnetic radiation (EMR) system orapparatus 10 for irradiation of living tissue or tissue simulatingmaterial comprises generally an EMR or microwave generator or source 12to which is electrically connected, by a transmission means or line 16,EMR irradiating means 14.

Included in the irradiating means 14 are an applicator or applicatormeans 18 and broadband transition means 20 for providing substantiallyreflectionless EMR transmission between the transmission line 16 and theapplicator 18, as more particularly described below.

Additionally comprising the EMR apparatus 10 are thermal monitoring andcontrol means 22 and frequency monitoring and control means 24.

The thermal monitoring and control means includes one or moretemperature probes 30, for example, nonperturbating thermocouples, formonitoring tissue or test specimen temperatures during EMR irradiation.Thermal control means 32 to which the temperature probes 30 areelectrically connected are preferably of a programmable type by means ofwhich temperature-time irradiation profiles can be preselected, thecontrol being connected to the generator 12 to control operation thereofto achieve the preselected profile.

EMR frequency output of the generator 12 may be controlled by thefrequency monitoring and control means 24 which includes, for example, avoltage standing wave ratio (VSWR) meter connected by a line 34 into thetransmission line 16 adjacent to the generator 12 for measuring EMRenergy reflected theretowards. The frequency control means isparticularly useful in uses requiring reflected EMR energy to be at aminimum or below a preselected minimum when the reflected energy is afunction of applied energy, for example, in operation of whole body typeapplicators, as described below.

Both the thermal and frequency and monitoring control means 22 and 24are considered to be of conventional configuration and form no part ofthe present invention.

Because, as described below, impedances are closely matched throughout,the apparatus 10 has good efficiency throughout a broad dynamicfrequency range, or bandwidth ratio of at least 5 to 1, and preferably10 to 1. Accordingly, most of the electromagnetic energy provided by thegenerator 12 is applied by the applicator 18 to tissue or tissuesimulating test specimens. In this regard, as used herein the termtissue is understood to include all the various constituents of the bodysuch as skin, fat, muscle, bones and organs.

Since the generator 12 is not required to generate very much more EMRenergy than is required to be applied by the applicator 18, relativelylow cost generators can be used. As an illustration, the generator maybe a model 15152 radio frequency power generator available from theMicrowave Components Laboratory Company. Such type of generator 12 has atypical power output of 100 watts and operates over a frequency range ofabout 10 MHz to 2500 MHz as has been found useful in many applications.However, for applications requiring higher power levels or differentfrequency ranges, other, comparable generators may alternatively beused, higher power generators being available, for example, from theabove mentioned company.

As noted, the generator 12 should have a dynamic frequency range of atleast 5 to 1 and preferably 10 to 1 to enable broadband systemoperation, as is desirable to investigate such EMR hyperthermia effectsas heating at different frequencies, EMR penetration in different tissuecompositions, as well as such other medically related effects as heatingbodies or portions thereof after hypothermia conditions(such as lowtemperature operations). Broad band operation also enables investigationof low level, nonthermal EMR effects at all desired hyperthermiafrequencies.

Relatively high efficiency of the EMR apparatus 10 is achieved in largepart, over the broad dynamic frequency range of operation, by matchingimpedences throughout as closely as possible. Towards this end,characteristic impedences, Z_(o), of transmission portions, includingthe line 16, the transition means 20 and the applicator 18 are selectedto match the characteristic impedence of the tissue or tissue simulatingmaterial to be irradiated.

As used herein, and as generally defined, characteristic impedence,Z_(o), is that impedance which a transmission line infinite in lengthpresents at an input end thereof. When a transmission line which isfinite in length is terminated in an impedance equal to the linecharacteristic impedence, the line appears, insofar as EMR appliedenergy if concerned, as infinite in length. The importance of atransmission line appearing infinite in length to applied energy is thatno EMR reflections occur.

Since the apparatus 10 is configured for irradiating, particularly in amedical research environment, living tissue, such as animal or humantissue, or simultaneous thereof, the characteristic impedence of humantissue is selected as the characteristic impedence to be matchedthroughout.

Although different portions or layers of human tissue are considered tohave different impedences, depending largely upon water content, averagetissue impedence, at least over an approximate frequency range of 50 to2000 MHz, has been determined to be approximately 50 ohms. This value oftissue impedence conveniently permits use of conventional 50 ohm coaxialcable for the transmission line 16 and also to use generally standar EMRgenerators having 50 ohm output impedences over the entire selecteddynamic frequency range.

Accordingly, as described below, at least parallel plate input orlaunching portion of the applicator 18 are configured to have 50 ohmcharacteristic impedences over the entire selected frequency range. Alsoas described below, the transition means 20 is configured to have acharacteristic impedence of 50 ohms throughout the dynamic frequencyrange.

Assuming the transmission line 46 is coaxial in configuration, as seenin FIG. 2, such line comprises cylindrical inner and outer conductors 44and 46, respectively, which are separated by a dielectric layer 48. Aninsulating layer 50 surrounds the outer conductor 46. Ends of thecoaxial cable are terminated in conventional fittings or connectors 52.The connector 52 at an input end of the coaxial cable is shown, in FIG.1, connected to a conventional coaxial tee fitting 54 at the generator12. The line 34 associated with the frequency monitoring and controlmeans 24 is also shown connected to the same fitting 54.

Further assuming, for the type of applicators described herein, thatinput portions or launching means 64 included in the applicators areparallel plate in configuration, coaxial to parallel plate transition isrequired. However, direct stepping from coaxial to parallel platetransmission line configuration, for example, by using conventionalcoaxial bulkhead fittings, may cause an excessively abrupt step, evenwhen the lines themselves have the same characteristic impedances. Thisstep results from abrupt geometric changes. As a result, such abruptcoaxial to parallel plate connections can cause local higher order modeswhich generally result in excessive stray radiation and lowerefficiency. These transmitters typically have very close and criticalspacing between the parallel plates, such spacing also limiting themaximum power capability.

Accordingly, although conventional bulkhead fitting transitions havingthe stated deficiencies could be used, the transition means 20 isspecifically configured to provide Z_(o) matching interconnectionbetween the line 16 and parallel plate launching means 64, which issubstantially EMR reflectionless over the entire selected dynamicfrequency range.

In general, such Z_(o) matching is achieved by configuring a smoothlycontinuous and comparatively gradual mechanical and electricaltransition of outer and inner conductors 66 and 68, respectively, of thetransition means 20 from a coaxial input end configuration to a parallelplate output (or EMR launching) end configuration, as shown in FIGS. 2and 3. Such transition is specifically configured not only to provide acomparatively gradual transition but also to maintain a constant Z_(o)of 50 ohms (for the example described) at all transverse sectionsthereof.

It should be understood that for purposes of description herein, and asis generally accepted in the industry, the term "parallel plate" asapplied to two conductor transmission line does not require that planesof the conductors actually be parallel throughout. All that is requiredfor conventional parallel plate transmission line analysis to apply isthat the two conductors, as seen in all transverse cross sections,appear parallel. As long as this condition is met, actual planes of theconductors may diverge, as described below, or may converge.

Configuration of the transition means 20 to achieve constant Z_(o)coaxial to parallel plate transition is accordingly governed by coaxialand parallel plate transmission line equations and/or design curves. Fora two conductor coaxial cable, characteristic impedance, Z_(o), isexpressed by the well known formula: ##EQU1## In which e is thedielectric constant of the dielectric between the conductors, D is theinner diameter of the outer conductor and d is the outer diameter of theinner conductor.

Parallel plate transmission line design is governed by plots of Z_(o)versus conductor width (w) to spacing (h) ratio, as found, for example,in the MICROWAVE ENGINEERS HANDBOOK, Vol. 1, by Saad, published byARTECH HOUSE, INC. Generally for a given dielectric between theconductors, as the ratio w/h increases, Z_(o) decreases. Also, at aconstant w/h ratio, Z_(o) increases with decreasing dielectric constant.

For the foregoing equation (1), and referring to such plots asmentioned, it is seen that for air filled transmission lines (e=1), toachieve Z_(o) equals 50 ohms, for coaxial cables the ratio D/d mustequal 2.31 and for parallel plates the ratio w/h must equal about 5.

An additional factor considered, and described for illustrativepurposes, is that at least for low power levels, diameters of thecoaxial conductors are relatively small, for example D may be only about0.37 inches. As a result, smooth coaxial to parallel plate may bephysically difficult to achieve. In addition, to assist in visualinspection and evaluation of the transition means 20 after formingthereof, the transition means is preferably configured such that spacingbetween the conductors 66 and 68 at both the coaxial and parallel plateends is basically identical. This enables spacing between the conductors66 and 68 to be kept constant during the transition.

A further consideration is that for transition between a dielectricallyfilled coaxial cable (the line 16) and air filled parallel platelaunching means 64, compensation must be made for change in dielectricconstant.

This compensation is most easily made at the input end of the transitionmeans 20, assuming the transition means is to be air filled. Fromequation (1) is seen that for Z_(o) to remain constant when e changes,the ratio D/d must be changed. Assuming e of the line 16 is equal to 2.1and that the initial D of the conductors 66 is at the 0.37 inches of thecoaxial conductor 44, d of the transition means inner conductor 68 isstepped from the 0.11 inches of the coaxial inner conductor 46 to 0.16inches, thus, D/d equals 2.31 as is required for Z_(o) equal 50 ohms.Such stepping is most conveniently made at a transition means inputconnector 70.

To increase size of the conductors 66 and 68 and to achieve the desiredspacing, h, at the parallel plate end, the conductors are flaredoutwardly in a longitudinal, diverging region 72. Throughout the lengthof such diverging region 72, the ratio D/d for the conductors 66 and 68is maintained at 2.31 to keep Z_(o) constant at 50 ohms. Flairing of theconductors 66 and 68 is such that, at Point A, FIG. 2, D equals oneinch, d equals about 0.43 inches and spacing between the conductors is0.285 inches, which is equal to a selected initial parallel plateseparation, h.

In a longitudinal transition region 74, which extends from Point "A" toa Point "B", the conductors 66 and 68 are axially split along upperregions and are gradually opened out and flattened into parallel plateconfiguration (FIGS. 3(d)-3(g)). At Point "B", the outer connector 68 iscontinued, or connected to, a conductive lower plate 82 which forms anextension thereof, and the inner conductor 68 is similarly continuedinto, or connected to, a corresponding, opposing conductive upper plate84 which forms an extension thereof. As described below, the plates 82and 84 typically comprise the launching means 64 of the associatedapplicator 18.

Between the Points "A" and "B", transition of the conductors 66 and 68is thus made between an initial coaxial configuration in which D=1 inchand d=0.43 inches to a parallel plate configuration in which width, w,of the inner conductor 68 and the upper plate 84 at their junction isequal to 0.68 inches (one half the circumference of the inner conductorat Point "A") and initial spacing, h, between the plates 84 and 82 isequal to 0.14 inches (w/h=5). Width of the outer conductor 66 isnarrowed to about 21/4 inches for convenience, width of the bottom plate82 being non-critical so long as such width is not reduced below widthw.

As long as length, 1, (FIG. 2) of the transition region 74 is not lessthan D at Point "A" of the transition region 74, high transitionefficiency, as measured by the amount of EMR reflection, is attained bymaking the described smooth, relatively gradual transition of theconductors 66 and 68 from coaxial to parallel plate cross section.

Since, however, the transition outer diameter D, must always be lessthan about half of a wave length to prevent causing undesirablefrequency moding, at higher frequencies, for example above 10 GHz, anadditional factor may have to be considered to minimize or eliminate EMRreflection in the transition means 20. This factor involves the manneror rate at which Z_(o) changes as the conductors 66 and 68 are openedup.

As seen, for example, in the REFERENCE DATA FOR RADIO ENGINEERS, 5thEdition, published by Howard Sams and Co., the manner in which Z_(o)changes for a split line conductor is given by the expression:

    ΔZ.sub.o =0.03 θ.sup.2                         (2)

in which ΔZ_(o) is the change in Z_(o), and θ is the conductor openingangle (as seen in FIGS. 3(d)-(f) expressed in radians.

As an example of the manner in which equations (1) and (2) are appliedtogether to obtain a constant Z_(o) during configuring the transitionmeans Z_(o) for high frequencies, assume that θ=π radians (180°), asseen in FIG. 3(e). From equation (2), for θ=π, ΔZ_(o) is calculated tobe about 0.30 or 30%. That is, by opening the conductors 66 and 68 upthrough 180 degrees, Z_(o) as otherwise calculated by equation (1)increases by 30%. If the initial D/d of 2.31 for Z_(o) were maintained(both D and d obviously increase as the conductors 66 and 68 are openedup) Z_(o) at θ equals 180 degrees would be about 65 ohms.

To compensate for this Z_(o) increase with θ, the ratio D/d must bedecreased by an amount reducing Z_(o) calculated by equation (1) by 30percent, or to about 35 ohms. Thus D/d at θ=180° must be about 1.8rather than 2.31. In the example, given, this would change w to 0.87inches from 0.68 inches.

Simular changes in configuration of the conductors 66 and 68 to achievethe appropriate D/d ratio are made at all other angles of θ up to about270 degrees, (FIG. 3(f)), at which angle the conductors are close toparallel plate configuration.

The described application of equation (2) may also be used to determinetransition means configuration at lower frequencies if desired.

An additional example of providing constant Z_(o) transition betweencoaxial and parallel plate EMR transmission lines is seen in FIGS. 4 and5 for a dielectrically filled type of transition means 20a. Thisalternative transition means 20a is particularly useful in conjunctionwith dielectrically filled applicator means, described below.

Because the dielectric constant of the coaxial line dielectric layer 48is relatively low (2.1), dielectric material for the transition means20a having a constant in the range of about 7-12 is desirable, a valueof 7 being assumed for purposes of description herein.

From equation (1), it is apparent that for Z_(o) to remain constant whenthe dielectric constant is changed, the ratio D/d must be changed. Thus,as shown in FIGS. 4 and 5, when making an abrupt transition from theline 16 having a dielectric constant of 2.1 to the transition means 20awhich is to be filled with a dielectric having a constant of 7, whilemaintaining Z_(o) at 50 ohms, either D or d must be changed. Forillustrative purposes, an outer coaxial conductor 66a is accordinglystepped, in a region 72a, to approximately 0.9 inches while the diameterd, of an inner conductor 68a, is kept the same as that of the coaxialline inner conductor 46 at 0.11 inches, which provides about 0.4 inchesconductor spacing.

It should be noted that changing both D and d at the point where echanges generally yields unsatisfactory results.

Although the coaxial to parallel plate transition is otherwise generallymade in the manner described above for the air filled transition means20, the smaller diameter inner conductor 68a requires some variation.Since the inner conductor 68a is too small to be readily opened up andflattened out, a flat plate 86 of diverging width is fixed to the end ofsuch conductor at the start of a coaxial to parallel plate transitionregion 74a. As the split outer conductor 66a is opened up, width of theplate 90 is increased to maintain an approximately uniform spacingbetween all regions at the plate and the outer conductor.

Were the plate 86 not added to the inner conductor 68a, as the outerconductor 66a opened out and flattened, outer conductor edge regions 88(FIG. 5(d)) would be farther from the inner conductor 68a than centralregions 90, causing an uneven electromagnetic field and a change inZ_(o).

For the exemplary configuration, distance between side edges 92 of theplate 86 and adjacent outer conductor regions 88 is maintained at 0.4inches. For an opening angle, θ of, for example, 180°, width of theplate 86 is 0.13 inches. As θ is increased to about 270°, width of theplate 86 is increased to 0.3 inches. When the transition to parallelplate configuration is completed, plate width, w is 0.51 inches andplate separation, h is 0.4 inches, resulting in a w/h ratio of 1.28, asis required for a Z_(o) of 50 ohms at E=7. Width of the flattened outerconductor at Point B, when transition to parallel plate, configurationis complete, may be reduced to about 1.4 inches for convenience.

Some improvement in Z_(o) matching during the coaxial to parallel platetransition may be provided by curving the plate 86 so that thetransition is more nearly like that shown in FIGS. 2 and 3 for thetransition means 20 with the result that equations (1) and (2) can bedirectly applied.

Parallel plate ends of the plate 86 and the outer conductor 66a areshown (FIG. 4) connected to diverging plates 84a and 82a, respectively,which may form EMR launching or input portions 64a of an associatedapplicator 18a as described below. When construction of the transitionmeans 20a is completed, internal regions between the conductors aredielectrically filled, as shown in phantom lines in FIG. 5.

In a similar manner, virtually any other type of constant impedance,coaxial to parallel plate transition can be constructed, including thosetypes associated with coaxial and parallel plate lines filled withdifferent dielectric constant material. Also, in an analogous manner,primary mode transition, although not at constant Z_(o), may be effectedbetween coaxial and parallel plate transmission lines having differentcharacteristic impedances, as may in some instances be necessary ordesirable.

Furthermore, although the coaxial line 16 has been described asconnected to input ends of the transition means 20 and 20a, and theparallel plate conductors 82, 82a and 84, 84a as connected to outputends thereof, designation of input and output ends is arbitrary. Thatis, direction of EMR wave travel through the transition means 20 and 20ais immaterial, the transition means being bidirectional.

APPLICATOR MEANS

The air filled transition means 20 is particularly adapted for use withair filled applicators. Thus, in FIG. 6-9, the transition means 20 isshown connected to the diverging input region of EMR launching means 64associated with the applicator 18, which is of an air filled, wholebody, parallel plate type. Additionally comprising the applicator 18 isa terminating resonant chamber or resonator 96 configured for receivingand irradiating at least major portions of a body or body simulatingtest specimen. Together the transition means 20 and the applicator 18comprises the EMR irradiating means 14 of FIG. 1.

Forming the resonator 96 are parallel, opposing first and secondconductive plates 98 and 100, respectively, which are shown as formingupper and lower resonator surfaces. Electrically interconnecting, toshort together, remote ends of the plates 98 and 100 is a conductivefirst end wall 102. Although shown as completely closing an end of theresonator 96, the end wall 102 may be formed having one or more openingsthrough which portions of a body not intended to be irradiated mayproject.

A conductive, second partial end wall 104 is connected along an upperedge thereof to an input end of the first upper plate 98 to dependtherefrom. Preferably, as below explained, the second end wall 104extends at least about half way downwardly towards the second, lowerplate 100 so that the input end of the resonator 96 is at least halfclosed. A resonant cavity 106 is thereby defined in the resonator 96 bythe plates 98 and 100 and the end walls 102 and 104.

An output or launching end of the plate 84, which forms an upperconductive surface of the launching means 64, is connected to a loweredge 108 of the second end wall 104. A corresponding end of the plate82, which forms a lower conductive surface of the launching means 64, isconnected to, or formed continuously with, the resonator second, lowerplate 98. Width, w. of the upper plate 84 and separation, h, between theplates 82 and 84 are increased in a manner maintaining the ratio w/hequal to 5, as is necessary to maintain a constant Z_(o) of 50 ohms atall transverse sections of the launching means 94.

An EMR emitting or launching opening 110 is defined between the secondend wall edge 108 and the below adjacent intersection of the plates 82and 98. (FIGS. 6 and 7). When length of the resonator 98 is equal tohalf the wave length of radiation emitted through the opening 110,standing EMR waves will result in the cavity 106, the resonator thusacting as a half wave length termination to the launching means 84.

It is to be appreciated that when a body or test specimen is received inthe cavity 106, dielectric properties of the body or specimen cause theeffective or EMR apparent length of the resonator 96 to increaseslightly, the extent of such increase depending upon the extent to whichthe body or specimen fills the cavity 106, that is, upon the "fillfactor". The greater the fill factor, the greater the effective increasein resonator length will be. As a result, the applied frequency causingresonance varies with fill factor, and may be controlled by thefrequency means 24.

At the resonant frequency, when the fill factor is high, EMR energy israpidly absorbed from the standing waves, within several reflections, bya body or test specimen enclosed in the resonator 96. However, if thefill factor is so high that energy is rapidly absorbed in less thanseveral wave reflectors, non-uniform EMR heating of the body or specimentends to occur. If, on the other hand, the fill factor is low, anexcessive number of wave reflections between the resonator end walls 102and 104 occur before absorption, thereby permitting more radiationleakage from the resonator 96.

To reduce radiation leakage from the sides of the resonator 96,particularly when the fill factor is low or at frequencies other thanthe resonant frequency, conductive first and second partial side walls118 and 120, respectively, are connected in depending relationship toopposite sides of the upper plate 98, thereby partially closing sides ofthe resonator. Radiation leakage from the sides of the launching means64 is similarly minimized by conductive first and second partial sidewalls 122 and 124 which depend from side edges of the upper plate 84.Preferably the side walls 118, 120 and 122, 124 cover about half oftheir respective side openings.

The launching means 64 is configured to have a constant Z_(o) of 50 ohmsalong the length thereof, over the entire dynamic frequency range, as isnecessary for efficient broadband operation; however, an impedancemismatch occurs at the launching means--resonator interface because ofdimensional changes introduced by the second end wall 104 whichpartially defines the cavity 106.

If a w/h ratio of about two is assumed, as has been found both practicaland useful, for the resonator 96, when no body or specimen is receivedin the cavity 106, from the above mentioned w/h curves Z_(o) is 90, fore equals one. When the cavity contains a body or test specimen of humanshape having an assumed dielectric constant of about 49, resonator Z_(o)varies between approximately 35 to 90 ohms, because of the nonsymmetrical body shape.

An effect of the resulting Z_(o) step is that whenever the launchingmeans 64 radiates EMR energy into the cavity 106 through the opening110, some radiated energy is reflected back down the launching means.Additional emitted energy is reflected down the launching means 94 bythe end wall 102. Since, waves reflected from the end wall 102 areinverted, while those reflected by the Z_(o) step at the launchingmeans--resonator interface are not, reflected wave cancellation tends tooccur in the launching means. Thus, the Z_(o) step, caused in part bythe launching opening 110 being smaller than the input end of theresonator 96, provides a reflection cancelling effect.

Although the amount of the Z_(o) step can be varied by varying w/h ofthe resonator 96, to minimize total wave reflection down the launchingmeans 64 at a particular frequency narrow range of frequencies, totalreflection will be greater at other frequencies. Thus, efficiency, asmeasured by the amount reflected energy, varies with applied frequency.

Nevertheless, broadband capabilities of the launching means 64 are stillvery advantageous for investigating such variables as orientation ofloading the cavity 106, fill factors and resonator configuration.

By suitably dimensioning the resonator 96, a body loaded resonator Z_(o)of about 50 ohms could be obtained. However, some energy reflectionwould still occur, since stepping at the launching means--resonatorinterface of both resonator w and h would be necessary because ofdielectric change when the resonator 96 is loaded, assuming thepartially closed end wall is used to cause standing waves in theresonator.

Typically the amount of the Z_(o) step can be varied, by varying w/h ofthe resonator 96, to minimize the uncancelled EMR waves and totalreflected power.

An alternative, dielectrically filled, partial body EMR applicator 18a,which incorporates, at an input end, the dielectrically filledtransition means 20a is illustrated in FIGS. 10-12. Included in thedielectrically filled applicator 18a, which is in many respects similarto the above described air filled applicator 18, are input or launchingmeans 64a, corresponding to the air filled launching means 64. Suchlaunching means 64a has a conductive upper surface defined by the plate84a which is connected to the transition means center conductor plate86. A conductive lower surface of the launching means 64a is defined bythe plate 82a which is connected to the transition means outer conductor66a.

Both width, w, of the plate 84a of the launching means 64a andseparation, h, of the plates 84a and 82a diverge in a direction awayfrom the transition means 20a in a manner maintaining the ratio w/hconstant. Assuming the launching means 64a is filled or loaded with adielectric 130 having a dielectric constant of 7, as was above describedfor the transition means 20a, to keep Z_(o) constant at 50 ohms at alltransverse sections of the launching means, a w/h ratio of 1.28 ismaintained throughout.

Because the launching means 64a is dielectrically filled, under normaloperating condictions little side electromagnetic radiation into the airfrom between the plates 82a and 84a occurs. However, such leakage isminimized by connecting conductive, first and second partial upper sideplates 122a and 124a, respectively, along opposite side edges of theupper plate 84a. Similar conductive first and second partial lower sideplates 138 and 140, respectively, are connected along opposite sideedges of the lower plate 82a. In combination, the upper and lower sideplates 122a, 124a, 138 and 140 cover about half of the side areasbetween the plates 82a and 84a.

A flat, exposed irradiating or EMR launching surface 142 of thedielectric 130 is formed at an applying end of the launching means 64a.For illustrative purposes, the launching surface 142 is shown in FIG. 11in contact with an exposed surface 144 of a body or test specimenportion 146 to be irradiated by the applicator means 18a. Accordingly,the engaged body or specimen portion 146 functions as a termination ofthe applicator 13a, an average termination impedance of approximately 50ohms being thereby provided, as has been used in configurating portionsof the system to have characteristic impedances of 50 ohms.

Ordinarly the entire launching surface 142 cannot be placed in directcontact with the body or specimen surface 144, because of relativedifferences in size and shape. Consequently, small air gaps 148typically occur along edges of the launching surface 142 and tend tocause non-uniform coupling of the applied EMR field to the body orspecimen portion 146 and radiation leakage to the surroundings.

To improve coupling of the field from the applicator 18a into the bodyor speciman portion 146 and substantially reduce leakage effects of theair gaps 148, first and second conductive flaps 150 and 152 areelectrically connected, respectively, to output or launching ends of theplates 82a and 84a, to provide extensions thereof. Preferably, the flaps150 and 152 are pivotally connected to the plates 82a and 84a and areflexible or bendable to enable at least partially wrapping around thebody or specimen portion 146 and conforming to the surface 144 thereof.When the flaps 150 and 152 are "loaded" with the body or specimenportion 146 which functions as a dielectric, characteristic flapimpedance of about 50 ohms is maintained. The electric field,represented by field lines 158 in the region of the flaps 150 and 152for applied EMR waves traveling in the direction of Arrow "C" into theportion 146, (FIG. 11) indicate the manner in which the flaps, whichfunction as strip line transmission lines, couple the field into thespecimen.

This field coupling effect of the flaps 150 and 152 into the body orspecimen portion 146 is very important, and indicates an advantageousmanner in which two (or more) of the applicators 18a can be arranged inopposing relationship to form a radiating chamber 96a (FIG. 13). Whenthe respective flaps 150 and 152 are overlapped in the mannerillustrated, a resonant cavity 106a, which corresponds generally to thecavity 106 of the whole body resonator 96, is formed. As was describedfor an enclosed body in the resonator 96, the body or specimen portion146 enclosed in the resonator cavity 106a, dielectrically loads thecavity.

The illustrated dual applicator arrangement results in centralintensification of EMR power when both the applicators are emittingradiation having the same frequency, amplitude and phase. Accordingly,greater power is delivered in the central, flap overlapped region of thespecimen with resulting deeper heating of the body or specimen portion146 than normally occurs with use of only a single applicator.

Electrical shorting between opposing pairs of plates 82a and 84a andflaps 150 and 152 forming the applicator parallel plate or strip linetransmission line is prevented by an insulating layer 154 applied overall otherwise exposed exterior surfaces of the plates and flaps.

Although dimensions of the launching means 64a may be varied accordingto particular use intended, some limitations exist as to the separation,h, between the plates 82a and 84a. When such separation, h, approaches1/4 to 1/2 of the wave length of the EMR frequencies being applied, sideradiation leakage occurs and efficiency decreases. Consequently, as h isincreased, the upper limit of applied frequency must normally bereduced. Such limitation similarly applies to the air filled launchingmeans 64.

For a particular size of the applicator 18a in which the launchingsurface 142 is 5.30 inches wide (equal to w) and 4.12 inches high (equalto h) and with flaps 150 and 152 at least about 5 inches long,efficiency at various applied EMR frequencies has been measured andplotted (FIG. 14). To enable efficiency measurements, a pair of similarapplicators 18a were arranged in face-to-face relationship, withcorresponding launching surfaces 142 and flaps 150 and 152 in abutment.One of the applicators 18a was used to emit radiation over a frequencyrange from about 50 MHz to 500 MHz while the other was used as areceiving antenna.

Applicator efficiency, for the plot shown in FIG. 14, is defined by theratio of EMR power received by the receiving one of the applicators 18ato power applied to the emitting one of the applicators. As indicatedefficiency has a maximum of over 90 percent in the 100-150 MHz range.Above 150 MHz, efficiency decreased to about 55 percent at 500 MHz dueto plate separation, h, approaching a half wave length condition. Belowabout 100 MHz, efficiency also decreased as the amount of wavereflections increased, thereby affecting coupling between the twoapplicators.

Efficiencies, when the applicator 13a is actually used in the mannerintended, are expected to be higher than those shown, the efficiencycurve shown being considered to represent a minimum efficiency curve.Nevertheless, the relatively high efficiencies obtained over the 10 to 1dynamic frequency range demonstrate the broadband capabilities of theapplicator 18a.

Radiation leakage measurements made at power levels of about 50 wattsand at frequencies in the 260-275 MHz range indicated that radiationleakage levels at distances of more than about four inches from theapplicator 18a are less than about 10 MW per square centimeter.

Efficiencies and radiation leakage of the air filled launching means 64are expected to be similar to those of the dielectrically filledapplicator 18a.

Although measured levels of radiation leakage under the specificconditions noted are below levels currently considered hazardous, underother use conditions leakage may be higher and leakage monitoring isdesirable. And since the Federal Communications Commission has allocatedonly several discrete radio frequencies to diathermy and medical use,shielding of the system 10 or portions to prevent interference withcommunication may be required even if shielding to prevent hazardousconditions to users is not.

Although the applicators 18 and 18a are considered very efficientconsidering their broadband operational capabilities, improvements inapplicators are continually sought so that more controlled and moreuniform EMR fields can utimately be applied to human patients forhyperthermia treatments. For this purpose, as well as such beforementioned purposes of investigating EMR heating at different body depthsand at different frequencies and investigating occurance of irradiationhot spots in tissue, broadband EMR apparatus is extremely important.

Although there has been described above specific arrangements ofefficient, broadband electromagnetic radiation apparatus and relatedcoaxial to parallel plate transmission line transition means andparallel plate-type applicators in accordance with the invention forpurposes of illustrating the manner in which the invention may be usedto advantage, it will be appreciated that the invention is not limitedthereto. Accordingly, any and all modifications, variations orequivalent arrangements which may occur to those skilled in the artshould be considered to be within the scope of the invention at definedin the appended claims.

What is claimed is:
 1. Electromagnetic radiation apparatus, whichcomprises:(a) a plurality of applicators configured for irradiatingliving tissue and tissue simulating matter, each of said applicatorshaving a radiation emitting surface; and, (b) conductive means fixed toeach of the applicators adjacent said emitting surface, for providingradiation emitting extensions, said conductive means includingdeformable first and second flaps adapted to be positioned at leastpartially around the tissue or tissue simulating matter in substantialoverlapping relationship with at least one of the flaps of adjacent onesof the applicators to thereby enclose portions of the tissue or tissuesimulating matter within a cavity defined by the radiation emittingsurfaces and overlapping flaps.